The propagation of inverted Neel wall sections in a serial accessed memory system was proposed by L. J. Schwee in the publication "Proposal On Cross-tie Wall and Bloch-line Propagation In Thin Magnetic Films," IEEE Transactions on Magnetics, MAG 8, No. 3, pages 405-407, September, 1972. Such a memory system utilizes a ferromagnetic film strip of approximately 81% Ni-19% Fe approximately 350 Angstroms (A) thick in which cross-tie walls can be changed to Neel walls and Neel walls can be changed to cross-tie walls by applying appropriate fields. Associated with the cross-tie walls is a section of inverted Neel wall that is bounded by a cross-tie on one end and a Bloch-line on the other end.
In such a cross-tie wall memory system, information is entered at one end of the serial access memory system by the generation of an inverted Neel wall section, formed by a cross-tie on one side and a Bloch-line on the other, that is representative of a stored binary 1 or of a non-inverted Neel wall section (i.e., the absence of a cross-tie, Bloch-line pair) that is representative of a stored binary 0. Such information is moved or propagated along the cross-tie wall by the successive generation (and then the selective annihilation) of inverted Neel wall sections at successive memory cells along the cross-tie wall. In the D. S. Lo, et al, U.S. Pat. No. 3,906,466 there is disclosed a propagation circuit for the transfer of inverted Neel wall sections through successive memory cells along the cross-tie walls. In the L. J. Schwee U.S. Pat. No. 3,868,660; in a Naval Ordinance Laboratory Report NOLTR 73-185; in the publication "Cross-tie Memories Simplified by the Use of Serrated Strips," L. J. Schwee, et al, AIP Conference Proceedings, No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, published April, 1976, pages 624-625, and in the publication "Cross-Tie/Bloch-Line Detection," G. J. Cosimini, et al, AIP Conference Proceedings, No. 3, 23rd Annual Conference on Magnetism and Magnetic Materials, 1978, published March, 1978, pages 1828-1830, there have been published some recent results of the further development of cross-tie wall memory systems and of detectors for the readout of binary information that is stored therein.
In a cross-tie wall memory system, the selective generation and propagation of the digital data representing inverted Neel wall sections about associated cross-ties and Bloch-lines have been demonstrated in the laboratory. Additionally, it has been shown that the data track of a cross-tie wall memory system may be configured into a film strip having repetitive patterns of asymmetrically serrated edge contours. Such film strip configurations are disclosed in the L. H. Johnson, et al, U.S. Pat. No. 4,075,612 and the L. J. Schwee U.S. Pat. No. 3,868,660, and in the publication "Cross-tie Memories Simplified by the Use of Serrated Strips," L. J. Schwee, et al, AIP Conference Proceedings No. 29, 21st Annual Conference on Magnetism and Magnetic Materials, 1975, published April, 1976, pages 624-625. More recently it has been proposed to construct cross-tie wall memory systems from a plurality of data tracks, each of which is formed as a strip of isotropic magnetic film, i.e., a film having substantially zero uniaxial anisotropy. The data-track-defining strip of isotropic magnetic film utilizes its shape, i.e., its edge contour, induced anisotropy, rather than its easy axis magnetic field induced anisotropy, to constrain the cross-tie wall within the planar contour of the film strip. The use of the shape induced anisotropy of an isotropic strip of magnetic film permits the use of nonlinear, i.e., curved, data tracks which may be configured into cross-tie wall memory systems that perform both memory and logic functions. Such a system is disclosed in the E. J. Torok U.S. Pat. No. 4,075,613.
Although the generation, propagation and logic manipulation of inverted-Neel-wall-section-defining data bits and the detection or readout thereof have received considerable study, one area that can still use improvement in the development of a workable cross-tie wall memory system is the detector or the device that reads out the information that is stored in the cross-tie wall memory system. Many such detectors or readout devices have been found to be workable and are disclosed in the patent literature--see the D. S. Lo, et al, U.S. Pat. No. 4,001,795; E. J. Torok, et al, U.S. Pat. No. 4,024,515; E. J. Torok U.S. Pat. No. 4,024,516, and the E. J. Torok, et al, U.S. Pat. No. 4,034,359. The present invention is directed toward an improved method of and an apparatus for reading out the information that is stored in a cross-tie wall memory system.